First of all my apologies to bring again another topic about solid state relays. I've bought the starter kit and completed all the beginners projects included in the kit, so I think I have now what is required to start moving forward to something more close to a proper use of Arduino.

I'm thinking about buying some SSR to control some 230VAC devices (lamps mainly). I know how to choose them according to the main line voltage/amperage and also to the arduino's side "limitations". My question is about a way to find if the main circuit is connected from the arduino side. For example, if I decide to connect a SSR to a lamp and to the arduino how can I know if the lamp is turned on from the arduino if I switch the lamp on through a switch connected in paralel with the relay?

An SSR is a "special kind" of octocoupler, so it has a LED. Does this mean that if the main circuit is on (switched from the arduino or from the mechanical switch) the SSR led will always be on and that the value I get from the arduino digital pin is always HIGH? Or on the other I can only turn the SSR led on from the low DC power side?

...An SSR is a "special kind" of octocoupler, so it has a LED. Does this mean that if the main circuit is on (switched from the arduino or from the mechanical switch) the SSR led will always be on and that the value I get from the arduino digital pin is always HIGH? Or on the other I can only turn the SSR led on from the low DC power side?...

I think I got what you concerned. It is perfect point.

The led of SSR has life span. if SSR is on most of time, your idea will help a lot for extend led life span. and implementation is easy and just inverter opto-isolator. However at practical is no go, the deal stopper is low DC power side power failure will cause high AC side is on. It is not acceptable.

...I'm thinking about buying some SSR to control some 230VAC devices (lamps mainly). I know how to choose them according to the main line voltage/amperage and also to the arduino's side "limitations". My question is about a way to find if the main circuit is connected from the arduino side. For example, if I decide to connect a SSR to a lamp and to the arduino how can I know if the lamp is turned on from the arduino if I switch the lamp on through a switch connected in paralel with the relay?...

What you ask is AC voltage/current sensor or monitor. We have some thread about it, see if it is helpful, otherwise post back here we will sharp the pencil.

if SSR is on most of time, your idea will help a lot for extend led life span. and implementation is easy and just inverter opto-isolator. However at practical is no go, the deal stopper is low DC power side power failure will cause high AC side is on. It is not acceptable.

WTF is that supposed to mean? It is gobbledegook at best totally wrong at worst.

No it is a special term I reserve for members who give irrelevant and wrong advice persistently despite several previous warnings.

Let's try and pick the bones out of your comments. I will assume that you are not a native English speaker so lets not dwell on things like sentence construction although it does make things hard to read.

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However at practical is no go, the deal stopper is low DC power side power failure will cause high AC side is on.

A power failure on the DC side, I assume that is the LED side would not result in the AC side being on, it would result in the triac not being triggered and so no conduction would take place, the same situation as when it were off. So your comment here is just plain wrong.

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if SSR is on most of time, your idea will help a lot for extend led life span.

The LED in an SSR is the most reliable component in the circuit and so the least likely to fail so extending the life span on it is not going to affect the overall performance of the component.

PLAN FOnly post when you know what you are talking about. If you are not sure on a topic and still feel you would like to contribute then acknowledge the fact in a preamble, like I am no expert but ... or I think you might ....

Remember, I have told you before, this is a beginners forum and it is incumbent upon you to give clear, accurate, relevant advice, not flights of fancy.

From the OP

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Or on the other I can only turn the SSR led on from the low DC power side?

...Let's try and pick the bones out of your comments. I will assume that you are not a native English speaker so lets not dwell on things like sentence construction although it does make things hard to read.

You get that right;-English is my third one, among Chinese, Japanese.My next one and I wish not last one is;-

Remember, I have told you before, this is a beginners forum and it is incumbent upon you to give clear, accurate, relevant advice, not flights of fancy.

Totally disagree, Electronics is very board science, so many vertical field. I found a lot of OP has so deeply knowledge need me multiple lifetimes (I overestimate my skill, at most case I never) to catch. Might be that is your problem treat every one beside yourself as beginner.

You're allowed to disagree (but I'll reserve the right to disagree with you because it is a forum largely for beginners), but if you carry on posting content-deficient bollocks, and you'll find yourself on the wrong end of a ban.

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.Do not send technical questions via personal messaging - they will be ignored.

You're allowed to disagree (but I'll reserve the right to disagree with you because it is a forum largely for beginners), but if you carry on posting content-deficient bollocks, and you'll find yourself on the wrong end of a ban.

"content-deficient bollocks" ? I am more than happy to find out where?